Many diverse applications may benefit from an effective remote detection and characterization of airborne aggregations of particulates. For example, climate change studies have shown that cloud effects and aerosol-cloud interactions (i.e. aerosol, indirect effects) are among the largest uncertainties in simulations of climate change. Elastic backscatter lidars are highly sensitive instruments capable of providing profiles of clouds, aerosols, and other particulates aggregation structures within the atmosphere. An addition of polarization-sensitive detection provides information pertaining to the phase of cloud particulates and to the type of aerosol particulates. The U.S. DOE Atmospheric Radiation Measurements (ARM) Program has deployed eye-safe lidars for semi-autonomous operation at each of its climate research facilities for over a decade. Recently, polarization-sensitive lidar systems have been deployed by ARM through straightforward modifications of pre-existing designs and equipment.
Remote detection and stand-off characterization of chemical/biological agents may be a decisive factor in early warning chemical/biological systems allowing for improved survivability of personnel in the battlefield and/or other targeted or associated areas. One exemplary system incorporating a pulsed lidar operating using visible light is described by Lee, et al, “Micro Pulse lidar for Aerosol & Cloud Measurement”, Advances in Atmospheric Remote Sensing with lidar, pp. 7-10, A. Ansmann, Ed., Springer Verlag, Berlin, 1997, while a near IR, is described, for example, by Condatore, et al, “U.S. Army Soldier and Biological Chemical Command Counter Proliferation Long Range—Biological Standoff Detection System (CP LR BSDS)”, Proceedings of SPIE, Vol. 3707, 1999. the entire contents of which are incorporated herein by reference, have demonstrated the high sensitivity and long-range (up to 50 km) capability to detect aerosol clouds. Consequently, an aerosol lidar is a demonstrated technique for long-range detection and characterization of bio-warfare aerosols. Furthermore, similar lidar systems may be used for remote sensing and stand-off detection of air polluting aggregations of particulates generated by intentional commercial activities or accidentally released particulate aggregations.
The polarization switching lidar devices for remote detection and characterization of airborne aggregation of particulates in accordance with the present invention are essentially sensitive to the polarization relative to a predetermined plane of polarization. Therefore, any phase retardation that contributes to the same relative angle of polarization with respect to the predetermined plain of polarization cannot be resolved and are considered identical. More particularly, all phase retardation states having phase differences (“retardations”) Δφ=nπ radians (n=0, ±1, ±2, ±3 . . . ) are considered substantially equal and inclusively designated as a “zero retardation state”, while all phase retardation states having phase differences (“retardations”) Δφ=mπ/2 radians (m=±1, ±3, ±5 . . . ) are considered substantially equal and inclusively designated as a “quarter-wave retardation state” for the purposes of the further recitations.